Explanation
transactionsDf.groupBy("productId").count()
Correct. This code block first groups DataFrame transactionsDf by column productId and then counts the rows in each group.
transactionsDf.groupBy("productId").select(count("value"))
Incorrect. You cannot call select on a GroupedData object (the output of a groupBy) statement.
transactionsDf.count("productId")
No. DataFrame.count() does not take any arguments.
transactionsDf.count("productId").distinct()
Wrong. Since DataFrame.count() does not take any arguments, this option cannot be right.
transactionsDf.groupBy("productId").agg(col("value").count())
False. A Column object, as returned by col("value"), does not have a count() method. You can see all available methods for Column object linked in the Spark documentation below.
More info: pyspark.sql.DataFrame.count - PySpark 3.1.2 documentation, pyspark.sql.Column - PySpark
3.1.2 documentation
Static notebook | Dynamic notebook: See test 3